1. Field of the Invention
The present invention relates, in general, to a radial tire for an automobile, in which a lyocell cord with excellent dimensional stability at high temperatures and dry/wet tenacity ratio is applied to a carcass ply and, in particular, to a radial tire for an automobile, in which a fatigue resistance and dimensional stability are improved by applying the lyocell cord to a radial tire with low aspect ratio. The term xe2x80x9clyocellxe2x80x9d means a cellulose fiber, which has a much higher wet tenacity than viscose rayon.
2. Description of the Prior Art
A traditional radial tire comprises a carcass ply in which rubber is reinforced by fiber cords such as polyester, rayon, or aramid, a belt in which rubber is reinforced by steel cords, and a bead wire.
The bead wire for preventing the tire from bead unseating problem and maintaining structural integrity is positioned at a junction between the tire and the rim, and plays a role of fixing the carcass ply.
Originally, a pneumatic tire comprises cotton canvas cloth as a carcass ply, and later synthetic fiber cords such as rayon, nylon, and polyester were used as the carcass ply with the development of synthetic fibers.
The pneumatic radial tire, in particular, the pneumatic radial tire with an aspect ratio of 0.65 to 0.82, uses polyester as the carcass ply. On the other hand, rayon carcass ply is preferred when the pneumatic radial tire for high-speed driving has a low aspect ratio.
Recently, polyester is applied to the radial tire for high-speed driving with the low aspect ratio, however, the application is restricted because polyester has poorer thermal properties and dimensional stability than rayon.
Meanwhile, rayon has disadvantages in terms of its physical properties and production process, so that rayon is also limitedly applied to radial tires.
In other words, rayon is produced by use of an indirect substitution process, which is complicated and not environmentally friendly, so that the process has an disadvantage in view of recent tendency of attaching importance to protection of the environment. In addition, rayon cords are not suitable to use as the tire cord because its wet strength is too low, and the tenacity of the tire is reduced owing to the moisture penetrated into the tire through a crack or wound in the tire""s tread during use of the tire, so that durability of the tire is reduced. Also, a moisture regain should be controlled to 2% or lower during production of the tire.
Therefore, a tire using rayon carcass has been limitedly used even though rayon has excellent thermal properties and dimensional stability.
Therefore, it is an object of the present invention to provide a radial tire for an automobile having an improved fatigue resistance and structural integrity and low aspect ratio, by using a lyocell cord with excellent physical properties, dimensional stability and dry tenacity/wet tenacity ratio as a material of a carcass ply of a pneumatic radial tire.